Glossary of Terms

We know that many of the concepts used on this site can be difficult to understand. For that reason, we have provided you with a glossary to help you make sense of the terms used in Comparative Effectiveness Research. Every word that is defined in this glossary should appear highlighted throughout the Web site. When you come upon a highlighted term and would like to read the full definition, you can either click on the word to visit the glossary or roll your mouse over the word for a pop-up definition.

Definition: The number of people who would need to be treated over a specific period of time before one bad outcome of the treatment will occur. The number needed to harm (NNH) for a treatment can be known only if clinical trials of the treatment have been performed.

Example:

For example, a meta-analysis looked at the risk of death for people with Alzheimer's disease who were taking atypical antipsychotic medication. The researchers found that for every 100 people with Alzheimer's disease using atypical antipsychotic medication, there was one additional death compared to 100 people with Alzheimer's disease using placebo (Number Needed to Harm=100).